Help! iMac won't take my password

So I bought a new 27" iMac a few months ago and really haven't had time to mess with it. I'm finally getting around to transferring all my stuff from my old iMac. When I open migration assistant, it asks for my password and I type it in and it tells me it is wrong. It's the same password I have used since I bought that thing seven years ago. It says the only way to reset my password is to do a backup, restore my computer to its basic setup, and then do a restore from my backup. Is there another way to do this? I'm worried that something might happen and I'll lose everything on that computer. Or is there another way to transfer my iPhoto and iTunes library over without using the migration assistant? This has been really frustrating me. Thank you for any help.